Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$82.77	7.263%	$88.7816	$88.78	$88.80	$88.80
Purchase #2	$141.65	8.789%	$154.0996	$154.10	$154.10	$154.10
Purchase #3	$81.59	5.332%	$85.9404	$85.94	$85.95	$85.90
Purchase #4	$48.37	6.128%	$51.3341	$51.33	$51.35	$51.30
Purchase #5	$122.40	7.730%	$131.8615	$131.86	$131.85	$131.90
Purchase #6	$229.41	8.813%	$249.6279	$249.63	$249.65	$249.60
Purchase #7	$94.71	10.224%	$104.3932	$104.39	$104.40	$104.40
7 purchase totals =	$800.90		$866.0383	$866.03	$866.10	$866.00